A variety of systems have been devised for vehicle occupant protection. The most commonly employed systems have belts or harnesses to fasten about vehicle occupants, as well as inflatable air bags. These systems help to control occupant motion and absorb the occupant's kinetic energy during a vehicle collision.
Both upper and lower body protection can be achieved by purely "passive" systems. "Passive" refers to the fact that the occupant does not have any active participation in the actuation or application of the protection system. "Passive" systems include automatically applied seat belts and automatically actuated air bags and knee bolsters. One such passive protection system includes an air bag to help protect the upper torso and head of a vehicle occupant and a knee bolster to provide lower body restraint.